Gas-producing composition



GAS-PRODUCING COMPOSITION Aubrey Edward Harper, Glasgow, James Grigor, Coatbridge, and Edward Graham 'Cooke, West Kilbride, Scotland, assignors to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain No Drawing. Filed Mar. 12, 1957, Ser. No. 645,643

Claims priority, application Great Britain Apr. 21, 1956 8 Claims. (Cl. 52-.5)

This invention relates to improvements in or relating to gas-producing compositions and more particularly-to may be used to express this variation. When all factorsaffecting the rate of burningof a charge are kept constant with the exception of the initial temperature of the charge the equilibrium pressure generated in the vented vessel when said burning rate law is obeyed may be expressed by K l/l-n [14112] i where K is a constant depending on the shape and nature of the charge and the size of the venting orifice. For compositions with the same temperature coefficient C, it follows from the above equation that for a given temperature range the difference between the equilibrium pressures operative at two temperature levels of a charge is greatest for high values of n, and least for low values of n. It is desirable for many purposes, e.g. for charges for use in rocket motors that the operating pressure should be substantially constant over a considerable temperature range and much effort has been expended without success so far to find agents for compositions based on ammonium nitrate which effectively lower the pressure exponent n.

It has now been found that compounds of iron, nickel and cobalt are effective agents for lowering the value of n of ammonium nitrate charges capable of self-sustained non-detonating gas-producing reaction. According to the present invention ammonium nitrate charges capable of self-sustained non-detonating gas-producing reaction are characterized in that they include a minor proportion of at least one compound of a metal from the transition elements of the eighth group of the Periodic Classification of the elements, namely iron, cobalt and nickel.

Said ammonium nitrate charges are capable of selfsustained non-detonating gas-producing reaction preferably due to the inclusion therein of a compound of chromium as for instance chromium sesquioxide, a chromate or dichromate, particularly ammonium dichromate.

Compounds of iron, cobalt and nickel suitable in the v compositions of the invention include ferrous oxalate,

ferrous carbonate, ferrous sulphide, iron oxides, ferrous lactate, ferrous citrate, ferrous hydrogen citrate, ferrous Fee formate, ferrous tartrate, ferric oxalate, potassium ferric oxalate, nickel oxalate, nickel carbonate, nickel formate, cobalt hydroxide, cobalt chromate and cobalt oxalate. It is, however, preferred to include salts of organic acids on account of their superior properties. Of the three metals iron is preferred mainly on account of the superior activity of its salts and ferrous oxalate is particularly useful.

It would seem that it is usually desirable that the compositions of the invention should employ a potassium salt, that the effect of each agent depends on the oxygen value of the composition, and that if any particular ammonium nitrate gas producing composition has to be used it is usually necessary to determine by experiment which agent is the most suitable. Furthermore the charges of the invention need not contain a fuel if the agent is, for

instance, ferrous oxalate.

The amount of said compound included is normally of the order of 1 to 10% by weight of the composition. The optimum amount is dependent on the compound and on the nature and make-up of the remainder of the composition and also on the pressure range of interest. The charges of the invention can be given a low exponent n particularly for the range of pressures between 300 lb./ sq. in and 1000 lb./sq. in which range is particularly useful for rocket motor applications.

The invention is illustrated by the following examples in which all parts are byweight- Example 1 Pressed charges are made of the following compositions, namely 6 parts of a hydrocarbon wax, 92 parts of a 9:1 mixture of ammonium nitrate and potassium nitrate, 2 parts of ammonium dichromate and x parts of ferrous oxalate.

These charges are then made to undergo a self-sustained gas-producing reaction under different constant operating pressures in a vented vessel and the rate of burning at these different pressures measured. The loga rithm of each operating pressure is plotted against the logarithm of the corresponding burning rate and the slope of each straight portion of the graph produced gives the value of the pressure exponent n for each straight portion.

The effect of increasing concentration of ferrous oxalate in such charges is shown in the following table which relates concentration of ferrous oxalate and corresponding values of n at an arbitrary operating pressure of 400 lb./sq. in. (abs.).

Parts ferrous oxalate (1:) per parts of composition Pressure exponent n at 4001b./sq. in. (abs) Example 2 on the pressure exponent n for an arbitrary operating pressure of 400 1b./-sq. in. tabs.) is shown in the following table.

r P rr 4 ferric oxalate is omitted has a pressure exponent 0.51 at the same pressure.

A pressed charge is made having a composition 6 parts V of a hydrocarbon wax, 91 parts 9:1 ammonium nitrate/ potassium nitrate mixture, 3 parts chromium sesquioxide and 4 parts ferric oxalate. The pressure exponent n for this composition is 9.00 at an arbitrary operating pressure .01 400 lb/sqin. abswh lst .2 im lar cqmpsa tion from which the ferric oxalate is omitted has a pressure exponent n of 0.50 at the same pressure.

Example 6 sure of, .490 1 /sqin abs. whe e t e p e s exp e at e tcernpos here wh ch th votes,

. Example 7 Parts te ggzi sioo-tr 6 The effect of variation of initial temperatures of an tabs.) ammonium nitrate charge of composition 6 parts of a 4 hydrocarbon wax, 92 parts 9:1 ammonium nitrate/ 0.63 potassium nitrate mixture, and 2 parts ammonium digfgg chromate with and without 5 parts ferrous oxalate on 0. as 10 the operating pressure is carried out as follows. M0 Charges of 1.5 inch diameter are fired in a vented vessel so that the initial temperature of the charges lies the 1526111111118 3 range from 28 C. to 62 C. and the burning rates The eiiect on the pressure exponent n for an arbidetermmed {QT a *Senes of operanng f' ws- F trary operating pressure of 400 1b./sq. in. (abs) of iera s}? Peach temperalfure the f hm 9f ra rous oxalate at its optimum concentration in various 0f buIIl1Ilg 1S Plotted aga11 1$t the lPgaIlthm 0f e p ammonium nitrate compositions is shown in the followatlng pressure. A collection of 1111 g aphs t t ing table. same pressure exponent n can thus be obtained for said Pressure exponent Ammonium n at400lb./sq. in. Fuel, nitrate] Ammonium Ferrous tabs.) Fuel parts by potassium dichromate, oxalate,

weight nitrate (9 1) parts by parts by parts by weight weight Ferrous Ferrous weight oxalate oxalate present absent Anthraqulnone 12v 4 s5. 6 2. 0 5. 0 0. 00 0.08 p-Nitroani1ine, 1s. 14 78.86 3. o 5. 0 0. 00 0. 54 'An aniline-formaldehyde resin. 5.85 91'. 15 3. 0 5.0 0.00 0. 50 Terephth ica 18.7 78.3 3.0 4.0, 0.00 1.00 Trlnltrostilbene..- 20. 0 '17. o a. 0 5. 0 0. 00 0. 57 one 0 92.0 2.0 2.0 0.00 0.30

Example 4 range of charge temperatures. From these curves the The effect on the pressure exponent n for an arbi- 5 {ates of bqmmg tor Qagh charge temgermme at P my operating pressure of 400 lb./sq. in. stems W131 Pressure can be q A We 18 various agent's atria. sperm teammates a an new meme connestmg the reclpmcalrof these rates ammonium nitrate composition includes 6 of burning with the 'aPsolute tempera/mm pf the: ichairgg hydrocarbon wax as a fuel 2 parts ammonium dichro- The mammal 9f the Intercept of the gums so mate as catalyst and 9 2 parts of a 9'1 ammonium 40 on the absolute temperaiuxe axis is numfaricauy equal nitrate/potassium nitrate mixture and which in the abto the temperawre coemgent f thls value sence of an agent has a pressure exponent ri at an arbithe percentage change m .operanng .PFeSsure/ use any operating pressure a 400 lei/sq. is. (abs) of 0.66 (a) for anacharge of Sad rcomlzosltlqn a be is shown in the following table. lated b makmg u o th following q t o 46 T I: 1000' Y ressure k Additive Partsl'fiy exp0nentn" C welg -l The values of 1r thus obtained for said compositions Y e a Y with and without ferrous oxalate can now he used to 3 3: g gg Z-g 8 8g 5 calculate the change in operating pressure which will F rr'gus ei rateiuu .530 0300 es l fi om changin t h rg e p r om 2 gg g-g 8-3 to 62 C. This is illustrated in the following table F3333 ialate. liij 510 v013a whe ein the init a r t n pr u e a arbltranly statute 22. 8'23 Moe/sqasolue- Cobalt hydroxide 410 0110 55 Cobalt chromate 2. 0 0. operagpg calculated A t t o fi ii ii' fii it i ifi' n S 11 Example 5 ga me absyg rmu i (abs.);l .tial

temperature of temperature '0! charge 2;? $3. charge #6? O.

I s een trqms id ab e that t sham i pe at pressure between the temperaturelirnits of 28 C. and 62 C. is considerably less for the composition which includes ferrous oxalate in comparison with the compos t q wh eh ioesnot in ude f ou o a a Wha w s aim 1. In a conventional gas-producing composition caabl 9 sel -sus ai ed oi -d w i s sas-P q sin Bas en ens consis ng e n i y o mmo um n t he. movem n .sqmrr ns the add t o to sai we posi on of from about 1%'to 10% by weight of a salt fe rou ox l t srlatsi E u m h g o p cons ing ferrous malate, ferrous glycolate, ferrous carbonate, ferrous sulphide, ferrous lactate, ferrous citrate, ferrous hydrogen citrate, ferrous formate, ferrous tartrate, ferric oxalate, potassium ferric oxalate, nickel oxalate, nickel carbonate, nickel formate, cobalt hydroxide, cobalt chromate and cobalt oxalate, and a potassium salt selected from the group consisting of potassium nitrate and potassium dichromate.

2. A gas-producing composition as claimed in claim 1, which includes a fuel selected from the group consisting of hydrocarbon wax, anthraquinone, p-nitroaniline, an anilineformaldehyde resin, terephthalic acid, and trinitrostilbene.

3. A gas-producing composition as claimed in claim 2 which includes a compound of chromium, selected from the group consisting ,of chromium sesquioxide, ohromates and bichromates.

4. A gas-producing composition as claimed in claim 3 wherein the compound of chromium is a bichromate. 20

References Cited in the file of this patent UNITED STATES PATENTS 2,159,234 Taylor May 23, 1939 2,637,274 Taylor et a1. May 5, 1953 2,712,989 Maisner July 12, 1955 2,740,702 Mace Apr. 3, 1956 

1. IN A CONVENTIONAL GAS-PRODUCING COMPOSITION CAPABLE OF SELF-SUSTAINED, NON-DETONATING, GAS-PRODUCING REACTION AND CONSISTING ESSENTIALLY OF AMMONIUM NITRATE, THE IMPROVEMENT COMPRISING THE ADDITION TO SAID COMPOSITION OF FROM ABOUT 1% TO 10% BY WEIGHT OF A SALT SELECTED FROM THE GROUP CONSISTING OF FERROUS OXALATE, FERROUS MALATE, FERROUS GLYCOLATE, FERROUS CARBONATE, FERROUS SULPHIDE, FERROUS LACTATE, FERROUS CITRATE, FERROUS HYDROGEN CITRATE, FERROUS FORMATE, FERROUS TARTRATE, FERRIC OXALATE, POTASSIUM FERRIC OXALATE, NICKEL OXALATE, NICKEL CARBONATE, NICKEL FORMATE, COBALT HYDROXIDE, COBALT CHROMATE AND COBALT OXALATE, AND A POTASSIUM SALT SELECTED FROM THE GROUP CONSISTING OF POTASSIUM NITRATE AND POTASSIUM DICHROMATE. 